The very idea that science best expresses its authority through
consensus statements is at odds with a vibrant scientific enterprise.
Consensus is for textbooks; real science depends for its progress on
continual challenges to the current state of always-imperfect knowledge.
Science would provide better value to politics if it articulated the
broadest set of plausible interpretations, options and perspectives,
imagined by the best experts, rather than forcing convergence to an
allegedly unified voice.

Yet, as anyone who has served on a consensus committee knows, much
of what is most interesting about a subject gets left out of the final
report. For months, our geoengineering group argued about almost every
issue conceivably related to establishing a research programme. Many
ideas failed to make the report — not because they were wrong or
unimportant, but because they didn't attract a political constituency in
the group that was strong enough to keep them in. The commitment to
consensus therefore comes at a high price: the elimination of proposals
and alternatives that might be valuable for decision-makers dealing with
complex problems.

Some consensus reports do include dissenting views, but these are
usually relegated to a section at the back of the report, as if
regretfully announcing the marginalized views of one or two malcontents.
Science might instead borrow a lesson from the legal system. When the
US Supreme Court issues a split decision, it presents dissenting
opinions with as much force and rigour as the majority position. Judges
vote openly and sign their opinions, so it is clear who believes what,
and why — a transparency absent from expert consensus documents. Unlike a
pallid consensus, a vigorous disagreement between experts would provide
decision-makers with well-reasoned alternatives that inform and enrich
discussions as a controversy evolves, keeping ideas in play and options
open.

Not surprisingly, Dan and I have come to similar conclusions on this subject. Back in 2001 in Nature I wrote (PDF):

[E]fforts to reduce uncertainty via ‘consensus science’ — such as scientific assessments — are misplaced. Consensus science can provide only an illusion of certainty. When consensus is substituted for a diversity of perspectives, it may in fact unnecessarily constrain decision-makers’ options. Take for example weather forecasters, who are learning that the value to society of their forecasts is enhanced when decision-makers are provided with predictions in probabilistic rather than categorical fashion and decisions are made in full view of uncertainty.

As a general principle, science and technology will contribute more effectively to society’ needs when decision-makers base their expectations on a full distribution of outcomes, and then make choices in the face of the resulting — perhaps considerable — uncertainty.

In addition to leaving behind much of the interesting aspects of science, in my experience, the purpose of developing a "consensus" is to to quash dissent and end debate. Is it any wonder that policy discussions in the face of such a perspective are a dialogue of the like minded? In contrast, as Sarewitz writes, "a vigorous disagreement between experts would provide
decision-makers with well-reasoned alternatives that inform and enrich
discussions as a controversy evolves, keeping ideas in play and options
open."